Primary aluminum-air battery

ABSTRACT

An aqueous electrolyte aluminum-air battery comprises one or more cells, each cell comprising a frame which defines an electrolyte chamber. The frame is made of a rigid material inactive to the electrolyte. The cell has a consumable aluminum anode and an air cathode spaced from the anode by said electrolyte chamber. Means are provided for admitting electrolyte solution into the electrolyte chamber. A vent exposes the electrolyte chamber to atmosphere. A hydrophobic membrane which is impermeable to the passage of the electrolyte but permeable to the passage of hydrogen closes the vent. A surface of each cell anode is exposed to the flow of air. The amount of surface exposed is effective to dissipate heat generated at the anode.

BACKGROUND OF THE INVENTION

The present invention relates to a primary, aluminum-air battery and toa novel cell for such battery comprising a consumable reactive aluminumanode and an air cathode. The battery of the present invention remainsinactive until a liquid electrolyte, such as an alkali electrolyte asexemplified by sodium hydroxide or potassium hydroxide, is introducedinto the space of each cell between the aluminum anode and the aircathode. The cells of the present invention are mechanicallyrechargeable, e.g., by replacement of a spent aluminum anode with afresh anode, or by addition of fresh electrolyte, typically afterremoval of spent electrolyte, or by replacement of both anode andelectrolyte.

DESCRIPTION OF THE PRIOR ART

U.S. Pat. No. 4,246,324 discloses a plurality of box-like elements eachused to support an air cathode and a replaceable, consumable metal anodein spaced relationship with the air cathode. The elements are positionedwithin an outer tank which holds an aqueous electrolyte. Air, oxygen orother depolarizing gas is circulated through the interior of each of thebox-like elements to each air cathode. The air cathodes have a surfaceimpregnated with a hydrophobic material to make the cathodesubstantially impervious to the aqueous electrolyte. The gas pressurewithin the box-like elements is regulated so that liquid electrolytedoes not flood the pores of the cathode. It is indicated in the patentthat zinc is the preferred anode material, but that other consumableanodic materials such as iron, lithium, and cadmium can be used.

A similar arrangement of components in which the electrolyte iscontained within a tank, and the electrodes are suspended within theelectrolyte, is disclosed in U.S. Pat. No. 4,389,466. A preferred anodemetal in U.S. Pat. No. 4,389,466 is aluminum.

An aluminum-air battery which is commercially available and is disclosedin U.S. Pat. No. 4,626,482 comprises essentially an open vessel whichcontains an aqueous salt electrolyte. An aluminum anode and the aircathode are suspended in the electrolyte. The electrolyte is added tothe vessel at the time of use, and is poured from the vessel toinactivate the battery. This battery is used for emergency light.

A larger version of this battery is available in which the electrolyteis an aqueous solution of an alkali metal hydroxide, such as potassiumor sodium hydroxide. Pumps are employed to circulate the electrolytewithin the battery and to provide for heat dissipation. The electrolyteis open to atmosphere, and venting the battery is not a problem.

An advantage in the use of a metal-air couple of this type over otherprimary cell or dry cell batteries is that the cathode uses oxygenderived from air giving a metal-air couple a higher energy density. Analuminum-air couple has the further advantage over, for instance, azinc-air couple or an iron-air couple, in that the aluminum-air couplehas a higher cell voltage and higher energy yield per unit weight orunit volume of the anode. In addition, the anode reaction product in analuminum caustic electrolyte cell is a fine precipitate and is easy tohandle compared to the gell-like reaction product of a zinc-air cell.However, an aluminum-air couple has the disadvantage that it cangenerate a large amount of heat which can exceed the heat capacity ofthe electrolyte within the battery cell within a short period of timeand cause the electrolyte to boil.

Accordingly, it is an object of the present invention to provide acompact, bipolar, aluminum-air battery which is activated by theaddition of an aqueous electrolyte to a vented, essentially enclosedelectrolyte chamber for each battery cell.

It is also an object of the present invention to provide such analuminum-air battery wherein the aluminum anode provides a heat exchangesurface which is effective for the dissipation of heat generated in thebattery cell.

SUMMARY OF THE INVENTION

The present invention resides in an aqueous electrolyte aluminum-airbattery comprising one or more cells, each cell comprising a framedefining an electrolyte chamber. The frame is made of a rigid materialinactive to the electrolyte. Each cell comprises a consumable plate-likealuminum anode and an air cathode spaced from the anode by saidelectrolyte chamber. The air cathode is impervious to the flow ofaqueous electrolyte. Means are provided for admitting an aqueouselectrolyte into the electrolyte chamber. A vent exposes the electrolytechamber to atmosphere. A hydrophobic membrane impermeable to the passageof electrolyte at the pressure within the cell but permeable to thepassage of hydrogen closes said vent.

In an embodiment of the present invention, each cell anode has a surfaceexposed to the flow of convective air. The amount of surface exposed iseffective to dissipate heat generated at the anode.

Preferably, the aluminum-air battery of the present invention comprisesa plurality of cells mounted in a bipolar array. The battery comprisesspacers between the battery cells to provide inter-cell air spaces forthe flow of air across the anode of one cell and the air cathode of anadjacent cell. The spacers are electrically conductive and in electricalcontact with the anode of one cell and the air cathode of an adjacentcell.

Preferably, the aluminum anode is dimensioned with fin surfacesextending beyond the confines of each cell frame. Only relatively smallfins compared to the overall size of the anode are required to dissipateadditional heat from the electrolyte chamber.

In another preferred embodiment of the present invention, theelectrolyte is an aqueous caustic solution containing a surfactant. Apreferred surfactant is an anti-foaming agent.

In the practice of the present invention, it is contemplated that theelectrolyte can be added to the battery cells in measured amounts toactivate the battery for predetermined amounts of time, the batterybecoming inactive upon consumption of electrolyte. Activation of thebattery can be resumed by replacing spent electrolyte with freshelectrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the present invention will become apparent to thoseskilled in the art to which the present invention relates from readingthe following specification with reference to the accompanying drawings,in which:

FIG. 1 is an isometric view of an aluminum-air battery embodying thepresent invention;

FIG. 2 is an isometric partial section view of the cathode side of abattery cell of the battery of FIG. 1;

FIG. 3 is a section, elevation, side view of a battery cell of thebattery of FIG. 1;

FIG. 4 is a section view taken along line 4--4 of FIG. 3; and

FIG. 5 is a section view taken along line 5--5 of FIG. 3.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows an aluminum-air battery 12 of the present invention. Thebattery 12 comprises a plurality of cells 14 in stacked, contiguousrelationship held between bulkheads 16, 18. The bulkheads 16, 18 areoptional and function to support the stack of battery cells 14 spacedabove ground level and to insulate the battery stack from ground. Eachbulkhead comprises an L-shaped lower support member 20 and spaced apartarms 22 and 24 which extend upwardly from opposite ends of the lowersupport member 20. A metal current collector bar 26 extends between thearms 22 and 24, the bar 26 supporting in its center a battery terminal28. The lower support members 20 are of a non-conductive or insulatingmaterial, whereas the rest of each bulkhead 16, 18 is made of aconductive material. Examples of plastics which are non-conductive andsuitable for use as support members 20 are moldable or machinableplastics such as chlorinated polyvinyl chloride (CPVC), polysulfone,polytetrafluoroethylene, and acrylonitrile-butadiene-styrene (ABS). Onlybulkhead 16 on the lefthand side of battery 12 is fully shown in FIG. 1,bulkhead 18 on the righthand side of the battery having essentially thesame configuration.

The entire battery stack is assembled by extending tie rods 30 througheach of the bulkheads 16, 18 and the battery cells 14, in apertures 32(FIG. 4). In the embodiment shown in FIG. 1, there are six tie rods 30in spaced apart relationship defining a generally rectangularconfiguration, with three of the tie rods along each opposite side ofthe battery cell stack. The lower tie rods extend through the upstandingflanges 34 of the lower support members 20 in such a way as to hold thestack of the battery cells 14 spaced from ground level. Tie rod heads 36connected to opposite ends of the tie rods 30 hold the battery stack andbulkheads 16, 18 together.

The use of tie rods 30 is optional. The battery cells 14 can be heldtogether by other means, for instance, by simply gluing the batterycomponents together.

The battery elements, some of which have been referenced in FIG. 1, willnow be more particularly identified by referring to FIGS. 2 through 5,each battery cell 14 comprises a rectangular frame 40 somewhat in theshape of a window frame having side walls 42, 44 and bottom and topwalls 46, 48 (FIGS. 2, 3 and 4). The frame 40 is formed or moldedpreferably as one piece from a material of construction which isnon-reactive with chemicals present in the battery cell. Usefulmaterials of construction include ceramics, as well as plasticsincluding chlorinated polyvinyl chloride and polyphenylene oxide blendswith polystyrene, and combinations of the foregoing. The frame surface50 facing the front of the battery stack in FIG. 1 is the cathode sideof each battery cell and the frame surface 52 facing in the oppositedirection is the anode side of each battery cell.

Referring to FIGS. 3 and 4, the frame side walls 42, 44 and bottom andtop walls 46, 48 define a generally rectangular electrolyte chamber 54which extends, as shown in FIG. 3, between the cathode side 50 and theanode side 52. The top wall 48 is hollowed at 56 to provide anelectrolyte reservoir separate from the electrolyte chamber 54. Passages58 drilled in the top wall 48 extend vertically between the electrolytereservoir 56 and the electrolyte chamber 54 communicating theelectrolyte reservoir 56 with the electrolyte chamber 54.

A reservoir seal block 60 (FIGS. 2-4) seals the top of the electrolytereservoir 56. The seal block 60 has an elongated rectangular shape andis fastened to the top edge 62 (FIG. 2) of the frame top wall 48. Theseal block 60 can be fastened to the top edge 62 by any suitableadhesive, solvent welding, or other means. An elongated verticallyextending vent slot 64 extends longitudinally in the seal block 60 fromadjacent the lefthand side of the seal block substantially the fulllength of the block. A porous membrane 66 is positioned across the ventslot opening closing off the slot. The membrane is a hydrophobic/gaspermeable material which is porous to the passage of gases such ashydrogen gas, but is impermeable to the passage of water vapor andelectrolyte. The purpose of the membrane is to keep electrolyte andwater vapor in the reservoir 56 and the electrolyte chamber 54, butallow the escape of gases that may be generated within the electrolytechamber 54. If hydrogen gas, formed from parasitic corrosion of theanode by the caustic electrolyte, is not allowed to vent, it mayoverpressure the cell and possibly damage the air cathode. Additionally,the hydrogen may form a gas pocket between the electrodes which couldreduce the battery output.

One membrane 66 employed in the practice of the present invention is amembrane marketed by Norton Performance Plastics under the TrademarkZITEX. This is a fibrous-porous form of polytetrafluoroethylene (PTFE)which is inert to many chemicals including caustics, is thermallystable, and has non-wetting (hydrophobic) characteristics. The materialhas many filtering and venting applications, and has been used forventing lead/acid batteries.

In the embodiment illustrated, the seal block 60 is comprised of twopieces, an upper piece 68 and a lower piece 70. The porous membrane 66is sandwiched between the two pieces, which are fastened together by asuitable adhesive, solvent welding, or other means, holding the porousmembrane 66 in sandwiched relationship between the two pieces.

A fill hole 72 (FIGS. 1 and 4) is bored vertically through the sealblock and Provides access to reservoir 56 by which electrolyte fluid isintroduced into the reservoir, and from the reservoir into theelectrolyte chamber 54 by means of passages 58. Following filling, thefill hole is closed by a cap 74 (FIG. 4) threaded into the fill hole orotherwise held within the fill hole.

In practice, the reservoir 56 may be filled with electrolyte solution inaddition to the electrolyte chamber 54. This is desired becauseelectrolyte added to the reservoir is circulated by convection tochamber 54 increasing the capacity of the battery. When the electrolytebecomes saturated with aluminate from the reaction of the anode, thecell output will drop to zero.

At the bottom of the electrolyte chamber 54 in the frame bottom wall 46,an elongated sump 76 is formed. The sump 76 functions as a repositoryfor the collection of solid aluminate discharge product from thereaction at the anode.

A solid aluminum plate anode 80, which has a rectangular flatconfiguration, covers the anode side 52 of the electrolyte chamber 54.The plate 80 can be comprised of any suitable high performance, aluminumalloy having low polarization and low parasitic corrosion values. Suchalloys are well known and are disclosed, by way of example, in U.S. Pat.No. 3,379,636, in U.S. Pat. No. 4,751,086, and in patents cited therein.It is possible, by suitably alloying the aluminum, to obtain very lowcorrosion current values, for instance, ten (10) milliamps per squarecentimeter. The disclosures of U.S. Pat. Nos. 3,379,636 and 4,751,086are incorporated by reference herein.

Apertures drilled along the sides of the plate are aligned withapertures 32 in the battery cells. These apertures hold the platessecurely on the tie rods 30. A sealing adhesive or gasket 86 (FIGS. 2-5)is positioned between the anode plate 80 and the anode side 52 of eachframe 40 to seal the anode to the frame 40 and prevent the leakage ofelectrolyte from the electrolyte chamber 54 on the anode side of theframe. The adhesive or gasket should be stable to caustic. One suitableadhesive is an aluminum filled epoxy cement marketed by DevconCorporation under the trademark Devcon. If a gasket is used, it shouldbe resilient, typically low durometer. Suitable gasket materials areclosed cell EPDM, neoprene or vinyl.

An air cathode 90 seals the cathode side 50 of the electrolyte chamber54. High energy and high power yields are achieved in the presentinvention by the use of a high performance air cathode in combinationwith the high performance anode.

Details of a high performance air cathode suitable for use in thepresent invention are disclosed in prior Pat. No. 4,756,980, assigned toassignee of the present application. The disclosure of Pat. No.4,756,980 is incorporated by reference herein. The air cathode comprisesa thin, single sheet layer of catalyzed carbon particles, in mixturewith 10 to 50 weight percent of hydrophobic polymeric binder containinga fluorocarbon polymer. The sheet is free from hydrophilic bulk metalinternal to the sheet. Either or both the front or back flat surface ofthe sheet has pressed into it a foraminous current-conductive metal meshor screen. The metal screen is exposed at the sheet surface but isembedded into the surface. The metal screen is then sintered to thesheet at high temperature. Materials suitable for cathode screens aresilver plated copper wire, preferably copper wire which is nickel platedwith a silver plate top layer.

The sheet of catalyzed carbon particles and hydrophobic polymericbinder, being free of hydrophilic metal, has an open, porousconstruction receptive to the flow of air, but at the same time one thatis impermeable to the flow of aqueous electrolyte into the sheet pores.The metal screen gives the sheet mechanical strength and also functionsas a metallic current collector. For imparting even more strength to theair cathode, the cathode can be "double gridded" as disclosed in Pat.No. 4,756,980, with metal screen on both sides.

Another suitable high performance air cathode is also disclosed in U.S.Pat. No. 4,615,954, also assigned to the assignee of the presentapplication. The air cathode comprises at least two bonded compositelayers, one of which is a form-stable conductive wetproofing layer whilethe other is a thin active layer containing active carbon particles andhaving a high internal surface area, e.g., more than 1,000 m² /gram. Thedisclosure of this patent is also incorporated by reference herein.

In the embodiment illustrated, referring particularly to FIG. 2, the aircathode 90 is shown schematically as sheet 92 which it will beunderstood will usually be composed of a gas supplying layer as well asan active layer, with the active layer having catalyst containing carbonparticles in mixture with a polymeric binder. The air cathode 90 alsohas an outer foraminous, metallic, current collector screen 94 embeddedin the sheet 92. The sheet 92 and screen 94 are secured to the innerside of a rectangular cathode frame 98. The cathode frame 98, in turn,is secured within a rectangular seat 100 (FIG. 2) cut into the cathodeside 50 of frame 40 around the periphery of the electrolyte chamber 54.The cathode frame 98 is sealed into the seat 100 by the same epoxycement used for the anode or by other suitable means, so thatelectrolyte does not flow from the electrolyte chamber 54 on the cathodeside of the battery cell 14.

The foraminous metal current collector screen 94 has a width dimensionso that it extends beyond the side walls of the cathode frame 98, asshown in FIGS. 2 and 5, providing contact tabs 102. Between each batterycell 14, there is positioned a pair of metallic current conductingspacers 104 in the shape of upright bars. These spacers are similar inconfiguration to the upright bulkhead arms 22, 24 and are provided withapertures 106 (FIG. 2) which are aligned with those of the battery cell14 allowing the spacers to be mounted on the assembly tie rods 30. Eachof the spacers is provided with a raised surface 108. The raisedsurfaces 108 are positioned so that they connect the air cathode 90 withthe plate anode 80 of an adjacent cell 14 towards the cathode end of thebattery 12 (FIG. 1). The opposite side of each spacer 104 is in contactwith the air cathode contact tabs 102. This provides an electricalconnection between the cathode of one cell and the anode of the adjacentcell. The construction of the spacers 104, in addition, maintains aseparation between one cell and the adjacent cell which permits the flowof air into the space between the battery cells from all sides and intothe air cathode 90.

This construction provides oxygen to the cathode 90 and at the same timea convective air current which flows across the face of the aluminumplate anode 80 removing heat generated at the anode. The heat from theanode helps to increase the convection currents in the space between thecells provided by the spacers 104. Under ambient air conditions,sufficient heat may be removed through the plate anode 80 so that forcedair circulation in the space between adjacent cells can be avoided.However, forced air circulation may be desirable and especially whenoperating with air at elevated temperature.

With the air flow on one side, and with the electrolyte present on theother, the aluminum plate anode 90 serves as a liquid-air heat exchangesurface. Because of the cell construction, the air cathode 90 can alsoserve this purpose. During operation at ambient air temperature, it hasbeen found that normal convection currents will provide desirablecooling for inter-cell spacings of from about 0.2 inch to about 0.4inch, using at least substantially square anodes measuring from aboutone to two inches on a side. A ratio of inter-cell spacing to anode sidedimension of from about 1:2 to about 1:10, and more typically from about1:4 to about 1:8 will usually be serviceable under such conditions.Generally, where more elevated air temperature conditions might beencountered, such spacing to anode side dimension will be maintained,but forced air circulation will be utilized.

Without a means for dissipation of heat, the heat build-up can quicklyexceed the heat capacity of the electrolyte and cause the electrolyte toboil. By way of example, the cell efficiency is about 50 %. For eachwatt of power produced, a watt of heat is generated. But aluminum is agood heat conductive material. Also, as shown in the Figures, the sizeand shape of the anode 80 is such that it not only will completely coverthe electrolyte chamber 54, but preferably can extend even beyond thesidewalls 42 and 44 of the frame 40 providing exposed extensions 82. Inthe embodiment shown, the amount of the extension, or size of theextensions 82, is effective to provide a small surface area, e.g.,somewhat in the nature of a fin, for additional dissipation of heatgenerated at the anode.

The provision of even small extensions 82 beyond the side walls 42 and44 provides further heat dissipation. In the embodiment of the drawings,by way of example, the plate size is about two inches by a sidedimension of two and one-half inches. Extensions of about 1/4 inch toabout 1/2 inch in dimension extending beyond the side walls 42 and 44were found to be sufficient for further heat dissipation. Thus, on theorder of about 10 to about 30 percent of the surface area of the anode80 may advantageously comprise the extensions 82.

To assemble a cell stack, it is a simple matter to preassemble thebattery cells 14 (except for the anode plate 80) and then to mount aseries of the battery cells 14 with accompanying anode plates 80 andspacers 104 in the desired sequence on the six tie rods 30. Followingmounting of the battery cells on the tie rods 30, it is then a simplematter to install the bulkhead arms 22 and 24 at opposite ends of thebattery stack, and then to install the lower supports 20. The entireassembly is then held together simply by affixing the tie rod heads 34to the tie rods. Alternatively, the anodes 80 can be glue affixed to thecell frames 40 in a preassembly step prior to assembly of the cells 14on the tie rods 30.

Referring to FIG. 1, again only the bulkhead 16 and the L-shaped lowersupport member 20 at the cathode end of the battery 12 are fully shown.At the opposite anode end of the battery 12, the configuration issimilar to that at the cathode end except that it is adapted for contactwith an anode plate 80 and to provide an anode terminal.

Following assembly of a battery stack, the battery is activated by theintroduction of electrolyte into the electrolyte fill holes 72 of eachbattery cell 14. It is contemplated, in the practice of the presentinvention, that the electrolyte can be provided in measured amounts, forinstance, in pouches designed to introduce a predetermined amount ofelectrolyte to each battery cell, depending upon the length of timeduring which activation of the battery is required. The electrolytechamber 54 of each cell must be completely filled. The reservoir 56 ofeach cell can be completely filled or only partially filled.

Alternatively, the cells can be simultaneously filled from a manifold orother distribution device communicating with the fill holes of all ofthe cells.

In the practice of the present invention, the electrolyte is an aqueousliquid, e.g., a saline or a caustic liquid. Representative electrolytesinclude 6 to 10 molar aqueous sodium hydroxide or 6 to 10 molar aqueouspotassium hydroxide solution, with about a 7 to 8 molar potassiumhydroxide solution being preferred. A stannate solution such as anaqueous solution of sodium stannate, is added as a corrosion inhibitor,e.g., to provide the electrolyte with an about 0.02 to 0.2 molarsolution of the stannate. An electrolyte with an about 0.04 to 0.06molar solution of sodium stannate is preferred. During the period ofpower production, hydrogen bubbles form at the anode due to directreaction of the anode with the aqueous electrolyte. The hydrogen bubblesare very small and therefore the bouyant force of hydrogen in anelectrolyte is relatively low. To facilitate de-gasification of theelectrolyte, it is a concept of the present invention to add a smallamount of a surfactant to the electrolyte. One surfactant successfullyemployed for caustic electrolyte solutions is an anti-foaming agentmarketed under the trademark "DOWEX 1410" by Dow Chemical Co. Thisanti-foaming agent is a perfluorinated hydroxy ethylene. The compound isconventionally marketed by Dow Chemical Co. as an anti-foaming agent forcaustic compositions. It is used in the present invention in smallamounts, for instance at a level of from about 0.5 part per million(ppm) to about 20 ppm, with about 2-3 ppm being preferred.

An aspect of the present invention is the discovery that despite the useof a small amount of a surfactant, the hydrophobic porous membrane 66was still effective in retaining electrolyte and water vapor within theelectrolyte chamber 54 and reservoir 56.

Although the battery of the present invention is not rechargeablesimilar to a secondary battery, it is a simple matter to recharge thebattery. When electrolyte replacement is chosen for battery recharging,no battery disassembly will be required. Battery recharging may includereplacement of the aluminum anodes for the battery cells when the samebecome spent or too highly corroded. This is accomplished by simplydisassembling the battery stack by removing the tie rod heads and tierods from the stack. On removal of the tie rods, the spent anodes can bereplaced by fresh anodes, and the stack is then reassembled followingthe sequence set forth above with regard to initial assembly of thebattery stack. This provides a battery which has a dramaticallyincreased lifetime.

In the embodiment disclosed in the drawings, the battery cells arevented only at the top through the porous membranes 66. In thisembodiment, the battery cells are position sensitive in the sense thatthe cells have to be positioned so that the vent slots 64 are at thebattery's highest point. As an alternative, it is possible to providevent slots 64 on all four sides of the cell frames 40, covered with theporous membrane 66, thus decreasing the cell's position sensitivity. Afurther alternative is to make the entire frame 40 of the hydrophobic,gas permeable membrane material.

The battery cells 14 in the embodiment illustrated are connected inseries in the battery 12. It is contemplated that the batteries of thepresent invention will have principal use as a temporary power sourcewhere a high power output and light weight are essential. Examples ofapplications are electronic systems such as radio transmitters, andequipment for sonobuoys. The batteries would normally be used duringperiods when the primary power source is interrupted.

EXAMPLE 1

In this Example, ten cells 14 were assembled into a battery stack andwere connected in series to form a bipolar aluminum-air battery as shownin FIG. 1. The inter-cell gap was 0.25 inch. The electrolyte chamberdimensions were about one inch by one inch with an electrode gap ofabout 0.187 inch. The overall length of the battery was about 7.88inches. A cathode of the type disclosed in U.S. Pat. No. 4,756,980 wasused. The aluminum anode used, which had no extensions, measured, ininches, 1 7/16×1 7/16×0.09. The electrolyte was a 7.5 molar aqueouspotassium hydroxide solution containing 0.1 mole of sodium stannate and2-3 ppm "Dowex 1410" anti-foaming agent. About 5.5 milliliters ofelectrolyte was added to each cell.

The battery had an open circuit voltage of 15.68 initially, and anelapsed run time of about ninety minutes before the electrolyte wasexhausted. The battery was cooled by air convection with air at ambienttemperature (72° F.) with both the anode and the cathode serving as(electrolyte) liquid-air heat exchange surfaces. The temperature of theelectrolyte was maintained under these conditions within the range fromabout 33° C. to about 62° C.

EXAMPLE 2

In this Example, the battery of Example 1 was recharged by replacingspent electrolyte with fresh electrolyte. There was no anodereplacement. The battery had an initial open circuit voltage of 15.52.The total run time was eighty-one minutes. The current production was2.075 amp hours, or 0.377 amp hours per milliliter of electrolyte.

The battery was again recharged and gave an initial open circuit voltageof 15.62 volts. The battery ran for about ninety-two minutes and gave acurrent output of about 2.3 amp hours, or 0.418 amp hours/milliliter ofelectrolyte.

In both the second and third runs, the temperature of the electrolyteremained below about 70° C. The battery was determined to have anefficiency, defined as actual anode weight loss divided by theoreticalanode weight loss, of about 97.2 %.

EXAMPLE 3

A single battery cell of the battery of Example 1 was discharged underconstant resistance and compared with several commercially availablesingle cell batteries. The specific energy density and power densitiesare compared below:

    ______________________________________                                                                Watt-hr                                                      Weight           Watt-Hr                                                                              Per Cubic                                                                             Battery                                Battery                                                                              Grams   Watt-Hr  Per Gram                                                                             Inch    Size                                   ______________________________________                                        Alkaline                                                                             143     4.2      0.029  0.95    D                                      Ni-Cd  65      2.03     0.031          D                                      Al/Air 30.0    3.175    0.106  1.27    2" × 2"                                                                 by 0.5"                                                                       approx.                                ______________________________________                                    

From the above description of a preferred embodiment of the invention,those skilled in the art will perceive improvements, changes andmodifications. Such improvements, changes and modifications within theskill of the art are intended to be covered by the appended claims.

We claim:
 1. A cell adapted for utilization in an aqueous electrolytealuminum-air battery, said cell comprising:a frame defining anelectrolyte chamber having opposed sides, said frame being made of arigid insulating material inactive to said electrolyte; a consumablealuminum anode having a surface exposed to air currents external of saidcell; an air cathode spaced from said anode by said electrolyte chamber;means for admitting electrolyte solution into said electrolyte chamber;vent means exposing said electrolyte chamber to atmosphere; and ahydrophobic membrane permeable to the passage of hydrogen closing saidvent means.
 2. The cell as set forth in claim 1, wherein said anode is aflat plate, the dimensions of said plate being effective for dissipationof heat generated at said anode.
 3. The cell as set forth in claim 2,wherein said plate anode comprises extended surfaces extending beyondthe confines of said frame, said extended surfaces having aconfiguration effective for the dissipation of more heat generated atsaid anode.
 4. The cell as set forth in claim 3, wherein said extendedsurfaces constitute from about 10 to about 30 percent of the totalsurface area of said anode.
 5. The cell as set forth in claim 1, whereinsaid electrolyte is an aqueous saline or caustic electrolyte.
 6. Thecell as set forth in claim 1, wherein said electrolyte is a causticsolution comprising a surfactant, a corrosion inhibitor, or both.
 7. Thecell as set forth in claim 6, wherein said surfactant is an anti-foamingagent.
 8. The cell as set forth in claim 1, wherein said hydrophobicmembrane comprises fibrous polytetrafluoroethylene.
 9. The cell as setforth in claim 1, including an electrolyte reservoir spaced from saidelectrolyte chamber, and means communicating said reservoir with saidchamber.
 10. The cell as set forth in claim 1, wherein said cell isrecharged by addition of electrolyte to said electrolyte reservoir. 11.The cell as set forth in claim 1, wherein said cell is recharged byreplacement of said anode.
 12. A bipolar aluminum-air battery comprisinga plurality of the battery cells as set forth in claim 1, assembledin-series, including spacer means between each battery cell dimensionedfor circulation of air to each battery cell air cathode and across theexposed surface of each battery cell plate anode.
 13. The battery ofclaim 12, wherein said spacer means are electrically conductive and incontact with the air cathode of one cell and the anode of an adjacentcell.
 14. The battery of claim 12, wherein said cell anode has a surfaceexposed to air flow in an inter-cell space provided by said spacermeans, the dimensions of the anode exposed surface being effective forthe removal of heat generated at the anode.
 15. The battery of claim 14,wherein said spacer means provide an inter-cell spacing ratio relativeto an anode side dimension of from about 1:2 to about 1:10.
 16. Thebattery of claim 14, wherein said air flow is convective air flow. 17.The battery of claim 14, wherein said air flow is forced air flow.
 18. Acell for an aqueous electrolyte aluminum-air battery comprising:a framedefining an electrolyte chamber having opposed sides, said frame beingmade of a rigid insulating material inactive to said electrolyte; aconsumable aluminum plate anode; means affixing said anode to one sideof said electrolyte chamber, said anode having a surface exposed toconvective air currents external of said cell; an air cathode; meansaffixing said air cathode to the opposite side of said electrolytechamber; means for admitting a caustic electrolyte solution into saidelectrolyte chamber, said electrolyte solution containing a surfactant;vent means exposing said electrolyte chamber to atmosphere; and ahydrophobic membrane permeable to the passage of hydrogen closing saidvent means, said hydrophobic membrane retaining electrolyte solution andwater vapor in said electrolyte chamber; the dimensions of said anodebeing effective for the dissipation of heat generated at said anode. 19.In a cell for an aluminum-air battery wherein electrolyte is enclosed ina chamber and wherein the aluminum anode serves to contain saidelectrolyte in said chamber, the improvement comprising exposing asurface of said anode to air flow, the amount of surface exposed beingeffective to dissipate heat generated at said anode.
 20. The cell ofclaim 19, wherein said air flow is convective air flow or force
 21. Thecell of claim 19, wherein said air flow passes in heat exchangerelationship across the exposed surface of said anode.
 22. The cell ofclaim 19, wherein said anode is in the form of a plate comprisingextended surfaces extending beyond the confines of the electrolytechamber walls and said extended surfaces constitute from about 10 toabout 30 percent of the total surface area of said anode.
 23. The cellof claim 19, comprising vent means venting said electrolyte chamber anda hydrophobic membrane permeable to the passage of hydrogen closing saidvent means.
 24. The cell of claim 23, wherein said hydrophobic membranecomprises fibrous polytetrafluoroethnylene.
 25. An aluminum-air batterycomprising a plurality of battery cells as set forth in claim 19,wherein electrolyte is enclosed in a chamber of each cell and whereinthe aluminum anode of each cell serves to contain said electrolyte insaid chamber, said battery including a surface of each anode exposed toair flow, with the amount of surface exposed being effective todissipate heat generated at said anode.
 26. The battery of claim 25,including spacer means between the battery cells to provide inter-cellair spacers bounded on one side by a cell anode and on the opposite sideby an adjacent cell air cathode, the air flow in each inter-cell spacepassing in heat exchange relationship across the anode exposed surfaceand supplying air to said air cathode.
 27. The battery of claim 26,wherein said spacer means are electrically conductive and in electricalcontact with said anode and said adjacent cell air cathode.
 28. Thebattery of claim 26, wherein said spacer means provide an inter-cellspacing ratio relative to an anode side dimension of from about 1:2 toabout 1:10.
 29. In an aluminum-air battery comprising at least one cellwherein electrolyte is enclosed in a chamber in said cell with analuminum anode on one side and an air cathode on an opposite side,spaced apart one from the other and serving to contain said electrolytein said chamber, the improvement comprising a sump at the bottom of saidchamber extending between said anode and said cathode, said anode havinga surface exposed to air currents external of said cell.
 30. The batteryof claim 29, wherein said sump comprises an elongated slot extendingalong the length of said chamber.